CVD method for forming oxide-system dielectric thin film

ABSTRACT

The multi-source raw material are dissolved in the tetra-hydrofuran, in a liquid state and evaporated simultaneously and stably transported to the reactor, thereby the dielectric thin film used for capacitor having a good performance is formed with a good repeatability. The present invention provides CVD raw material for oxide-system dielectric thin film wherein organic metal raw material is dissolved in the tetra-hydrofuran and the metal atom of the organic metal raw material is selected at least among Pb, Ti, Zr or alkaline earth metal. As a result, a stable dielectric thin film can be formed by CVD method and the dielectric thin film can be used for a capacitor for memory devices.

This application is a divisional of application Ser. No. 08/367,745,filed Jan. 3, 1995, now U.S. Pat. No. 5,555,154, which is a file wrappercontinuation of application Ser. No. 08/121,341, filed Sep. 14, 1993,now abandoned.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to material for a chemical vapor deposition (CVD)method for forming an oxide-system dielectric thin film used for adielectric memory and a dielectric filter and the like, and also relatesto a capacitor for a memory device formed by the material.

2. Description of the Prior Art

In recent years, the integration of semi-conductor memory devices hasrapidly advanced. For example, regarding the dynamic random accessmemory (DRAM), bit number has increased at the sudden pace of, forexample, 4 times in 3 years.

This is because of attaining a high speed of device, and low consumptionpower and low cost. But, even if an integration degree is improved, acapacitor which comprises one of the elements in the DRAM must have acertain value of capacitance. From this reason, it is necessary to causethe film thickness of capacitor material to be thin. Therefore, thethickness of the thin film using SiO2 which has been used so far islimited for thinner film. If the dielectric constant increases bychanging material, it is able to obtain thinner film as well as acertain amount of capacity.

Accordingly, studies for the dielectric material which has a largedielectric constant and is used as a capacitor for a memory devicebecome the object of public attention these days.

Regarding the performance required for capacitor material, it has beenmost important that the material is a thin film which has a largedielectric constant and has a small leak current. That is, it isnecessary to use a large dielectric constant material and also a thinnerfilm and to make the leak current be minimum. For a general developmentaim, it is desirable that the SiO₂ equivalent thickness of the thin filmbe less than 1 nm and the leak current density be less than on the orderof 10⁻⁸ A/cm² when 1.65 V is applied to the thin film. For forming athin film on the capacitor electrode of the DRAM having stagedifference, it is profitable for the process to cause the thin film tostick well around the complex shape of the body using the CVD method.From the above points of view, an oxide-system dielectric thin film suchas tantalum-oxide, lead-titanium zirconate (PTZ),lead-lanthanum-zirconium titanate (PLZT), strontium titanate and bariumtitanate are examined for forming a thin film using all kinds of filmformation methods. Though it is most advantageous to form a film usingthe CVD method, it is troublesome that there is no material as a rawmaterial compound (referred to raw material, below) having goodstability and vaporization characteristics for CVD. This is because theis heating vaporization characteristics of the dipivaloyl-methane (DPM)compound of β-diketonate-system is principally not good, which is used alot as a raw material for CVD. It is pointed out that this is asubstantial defect caused by essential instability of the metal DPMcompound, for example, in the 52th Applied Physics Association Seminarpreliminary report No. 9a-P-11. As shown in the report No. 9a-P-11, theCVD method is still studied in spite of the above defect. It happens atan extreme occasion that the raw material has to be thrown away duringthe film forming when the raw material is unstable. Accordingly, whenthe raw material mentioned above has the defect, good performance of thedielectric thin film and good manufacturing repeatability are notobtained at present.

As described above, regarding the method for manufacturing anoxide-system dielectric thin film by conventional CVD method, since theCVD material has less stability and bad vaporization, it is impossibleto heat the CVD raw material at a low temperature and transport itstably to the CVD reactor.

Therefore, it is difficult to control the composition and also there isa big problem that a dielectric film can not be formed stably in orderto get good characteristics. On the other hand, if the raw material isheated at a high temperature in order to increase the vaporizationefficiency, thermal decomposition occurs during transporting the rawmaterial. Therefore, a crystallization failure of the film orcomposition drift inevitably occurs. In addition, the raw material isthrown away inconveniently as described above. If the composition(reaction) time becomes long by suppressing vaporization speed, thevaporization state of the raw material changes as time goes by.Therefore, the film composition becomes heterogeneous toward thethickness direction, and thus the leak current inevitably increases. Forthis reason, the development is strongly expected to obtain CVD materialhaving good and stable vaporization in a low temperature heating if theCVD material is used for a number of times and a long period. But, thereis still no further progress with respect to the technique.

Therefore, the CVD material for forming an oxide-system dielectric thinfilm of the present invention is invented to eliminate the above defectwhich occurs in raw material used in the conventional CVD. According tothe material of the present invention, it is different from theconventional material in that the conventional multi-source materialsneed to be separately vaporized, while in the present invention thematerial are liquidized and at the same time vaporized and transportedstably to the reactor. Accordingly, it is able to form the dielectricthin film for a capacitor having a good performance with goodrepeatability. DPM compound which is used frequently in the conventionalCVD method as described above, it is proved that these compounds of CVDraw material for oxide-system dielectric thin film capacitor of thepresent invention, especially, such as the alkaline earth metal of Baand Sr and the solid state compound of Pb and Ti, is not in a stablestate and also not in a good CVD reactor.

Therefore, it is difficult to control the composition and also there isa big problem that a dielectric film can not be formed stably in orderto get good characteristics. On the other hand, if the raw material isheated at a high temperature in order to increase the vaporizationefficiency, thermal decomposition occurs during transporting the rawmaterial. Therefore, a crystallization failure of the film orcomposition drift inevitably occurs. In addition, the raw material isthrown away inconveniently as described above. If the composition(reaction) time becomes long by suppressing vaporization speed, thevaporization state of the raw material changes as time goes by.Therefore, the film composition becomes heterogeneous toward thethickness direction, and thus the leak current inevitably increases. Forthis reason, the development is strongly expected to obtain CVD materialhaving good and stable vaporization in a low temperature heating if theCVD material is used for a number of times and a long period. But, thereis still no further progress with respect to the technique.

Therefore, the CVD material for forming an oxide-system dielectric thinfilm of the present invention is invented to eliminate the above defectwhich occurs in raw material used in the conventional CVD. According tothe material of the present invention, it is different from theconventional material in that the conventional multi-source materialsneed to be separately vaporized, while in the present invention thematerial are liquidized and at the same time vaporized and transportedstably to the reactor. Accordingly, it is able to form the dielectricthin film for a capacitor having a good performance with goodrepeatability. DPM compound which is used frequently in the conventionalCVD method as described above, it is proved that these compounds of CVDraw material for oxide-system dielectric thin film capacitor of thepresent invention, especially, such as the alkaline earth metal of Baand Sr and the solid state compound of Pb and Ti, is not in a stablestate and also not in a good vaporization state. Therefore, when theoxide-system dielectric thin film comprised of these metal oxide isformed by a CVD method, it is proved for a multi-source material that itis difficult to control an object composition and to form a filmcontinuously.

Accordingly, in the present invention, the inventors found that thecontrollability of the composition is improved and a dielectric filmhaving desired characteristic is formed continuously with goodrepeatability by dissolving these compounds in the solvent whichincludes tetra-hydrofuran as a main component for maintaining thesecompound stable for a long period in order to make one solution, and byevaporating the solution in a relatively low temperature heating withoutheat decomposition. Especially, in this invention, the repeatability forforming the film is remarkably improved in case that the film is formedcontinuously if liquid raw material is used when forming an oxide-systemdielectric thin film in the multi-component materials. Therefore, theperformance of the dielectric film is remarkably improved by using thedielectric film as a capacitor used for memory devises.

Regarding many kinds of organic solvents other than thetetra-hydrofuran, the inventors investigated in detail in relation tothe dissolving capacity of the material for composing the dielectricthin film comprised of the solid organic metal, (organometallic)compound, a evaporation characteristic of the solution and a long lifestability. The result shows that there found many solvents which coulddissolve the solid material well. But there found no good solvent havinggood heat vaporization and long life stability when making a solution bydissolving the raw material compound used as the dielectric filmcomprised of the organic metal compound such as the tetra-hydrofuran.

Therefore, the CVD raw material of the present invention is used forforming the oxide-system dielectric thin film having single ormulti-components, and which is liquid raw material in which at least onekind of organic material is dissolved in the tetra-hydrofuran and alsocan be attained in a stable state and in a good repeatability ofevaporation by heating. Especially, in the present invention, the sameraw material can be used for a number of times without reducing theevaporation characteristic, which was impossible to be carried out sofar.

The above explanation is also applied to liquid material in which theorganic metal compound is dissolved in the solvent including thetetra-hydrofuran.

It is desirable to use at least one kind of metals selected among Pb,Ti, Zr and alkaline earth metal as the metal atom of the organic metalcompound.

It is desirable to use a compound wherein the metal atom is coupled withorganic groups through oxygen atoms as the organic metal compound.

Regarding the compound wherein the metal atom is coupled with organicgroups through oxygen atoms, it is desirable to use at least one kind ofmetals selected among Pb, Ti, Zr and alkaline earth metal as the metalatom.

Regarding the compound wherein the metal atom is coupled with organicgroups through oxygen atoms, it is desirable that the metal atomcomprises Sr and/or Ba and Ti.

Regarding the compound wherein the metal atom is coupled with organicgroups through oxygen atoms, it is desirable to use acetyl-acetonates,dipivaloyl-methanates, alkoxides, hexafluoro-acetyl-acetonates,penta-fluoro-propanoil-pivaloyl-methanates, cyclopentadienyl which areselected at least among groups of Pb, Ti, Zr and alkaline earth metal,or one or more kinds of those derivatives.

Regarding the compound wherein the metal atom is coupled with organicgroups through oxygen atoms, it is desirable to use Sr and/or Ba and Tidipivaloyl-methanate system compound.

Regarding the compound wherein the metal atom is coupled with organicgroups through oxygen atoms, it is desirable to use Sr and/or Badipivaloyl-methanate system compound and Ti alkoxide.

Regarding the compound wherein the metal atom is coupled with organicgroups through oxygen atoms, it is desirable to use Sr and/or Badipivaloyl-methanate system compound and Ti iso-propoxide.

In the capacitor used for memory devises of the present invention, thedielectric film for the capacitor is formed by CVD method usingtetra-hydrofuran or CVD raw material for oxide-system dielectric thinfilm in which the organic metal compound is dissolved in the solventincluding the tetra-hydrofuran.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide a CVDraw material for oxide-system dielectric thin film having a goodperformance used for forming a capacitor.

According to one aspect of the present invention, there is provided CVDraw material for oxide-system dielectric thin film in which organicmetal compound is dissolved in tetra-hydrofuran.

Another aspect of the present invention, there is provided CVD rawmaterial for oxide-system dielectric thin film in which organic metalcompound is dissolved in solvent including tetra-hydrofuran.

Another aspect of the present invention, there is provided CVD rawmaterial for oxide-system dielectric thin film, wherein the metal atomof the organic metal raw material is one of the metals which is selectedat least among the group of Pb, Ti, Zr and alkaline earth metal.

Another aspect of the present invention, there is provided CVD rawmaterial for oxide-system dielectric thin film, wherein the organicmetal raw material is a compound in which the metal atom is coupled withorganic groups through oxygen atoms.

Another aspect of the present invention, there is provided CVD rawmaterial for oxide-system dielectric thin film, wherein the metal atomis Sr and/or Ba and Ti.

Another aspect of the present invention, there is provided CVD rawmaterial for oxide-system dielectric thin film wherein the raw materialcompound is one of acetyl-acetonates of metals selected among at leastthe group of Pb, Ti, Zr and alkaline earth metal dipivaloyl-methanatesof metals selected among at least the group of Pb, Ti, Zr and alkalineearth metal, alkoxides of metals selected among at least the group ofPb, Ti, Zr and alkaline earth metal, hexafluoro-acetyl-acetonates ofmetals selected among at least the group of Pb, Ti, Zr and alkalineearth metal, penta-fluoro-propanoil-pivaloyl-methanates of metalsselected among at least the group of Pb, Ti, Zr and alkaline earthmetal, cyclopentadienyl of metals selected among at least the group ofPb, Ti, Zr and alkaline earth metal, and one or more derivatives ofthose raw material compounds.

Another aspect of the present invention, there is provided CVD rawmaterial for oxide-system dielectric thin film, wherein the compound isa Sr and/or Ba dipivaloyl-methanate system compound and Tidipivaloyl-methanate.

Another aspect of the present invention, there is provided CVD rawmaterial for oxide-system dielectric thin film, wherein the compound isSr and/or Ba dipivaloyl-methanates and Ti alkoxide.

Another aspect of the present invention, there is provided CVD rawmaterial for oxide-system dielectric thin film, wherein the compound isSr and/or Ba dipivaloyl-methanates and Ti iso-propoxide.

Another aspect of the present invention, there is provided a capacitorfor memory devises which is formed by CVD method using CVD raw materialfor oxide-system dielectric thin film.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiment 1

An experiment was carried out using the ordinary hot wall type CVDequipment for investigating the vaporization of the raw material of theinvention. The raw material compound is acetyl-acetonate derivativecomprised of Sr and Ba having especially less vaporization and poorstability. The two materials are mixed to obtain two kinds of solutionsdissolved in the tetra-hydrofuran by 0.3 mol % concentration. Thedeposition quantity of the strontium oxide and the barium oxide on themagnesium oxide substrate are measured using weight method by heatingthe solution for a plurality of numbers of the continuous vaporizationat the temperature of 220° C. Further, the deposition quantity of thestrontium oxide and the barium oxide on the same substrate are measuredby heating the solution at the vapor temperature of 180˜240° C. forevery 20° C., using a weight method. The above respective depositionsare confirmed to be films of the oxide Sr or Ba using X-ray diffiction.

The deposition quantity of these three cases on the oxide magnesiumcircuit board of Sr oxide and Ba oxide are compared with the depositionquantity of the present invention in the following TABLE 1˜TABLE 4.

For comparison, the same raw material compound is dissolved in themethanol solution or acetone solution instead of the tetra-hydrofuran atthe same formation condition and using the same equipment. And the solidraw material organic metal compound without using organic solvent isused by CVD method.

As is apparent from TABLE 1 and 3, in case the CVD raw material of thepresent invention is used, the deposition quantity of oxide film morethan 20 times is obtained in comparison with the conventional solid rawmaterial organic metal compound, the methanol solution and the acetonesolution for the first vaporization at the same heating temperature.

In case of the raw material of the present invention, stable depositionquantity is obtained for further continuous vaporization. But, in caseof other raw materials, the deposition quantity of the oxide filmdecreases for the further number of continuous vaporization. As isapparent from TABLE 2 and 4, in case the raw material of the presentinvention is used, good deposition quantity of oxide film is obtained atany temperature in comparison with the other three solutions, becausethe present invention has good vaporization.

An experiment was carried out for investigating the deposition quantityunder the continuous vaporization over 10 times on the same conditionshown in TABLE 1 and TABLE 3. The result shows that in case of theconventional solid raw material organic metal compound, the methanolsolution and the acetone solution, the deposition quantity obtained fromthe evaporation of the raw material was not found at all after about 15times of heating. On the contry, in case of the raw material of thepresent invention, the deposition quantity of the oxide obtained fromthe vaporization of the CVD raw material is the same as that of thefirst experiment after the film formation of about 20 times has beencompleted. This state continued until the raw material is lost by theevaporation.

Embodiment 2

Another experiment was carried out using the same CVD equipment of thefirst embodiment. In the second embodiment, the raw material compound isPb dipivaloyl-methanate, Zr dipivaloyl-methanate and Tidipivaloyl-methanate, which are dissolved in the tetra-hydrofuran toobtain material solutions of the present invention. The atom ratio ofthe respective metal atoms of the raw material compound is obtained by anext equation.

    Pb:Zr:Ti=2.2:1:1

The concentration is 0.4 mol % for the entire solution.

An experiment for examining the vaporization of the present invention iscarried out as in the first embodiment. That is, the deposition quantityof the PZT system dielectric oxide on the platinum oxide substrate ismeasured by heating the material solution for a plurality of numbers ofthe continuous vaporization at the temperature of 200° C. Further, thedeposition quantity of the PZT system dielectric oxide on the samesubstrate is measured by heating the material solution at the vaportemperature of 180˜240° C. for every 20° C. vaporization temperature. Inboth cases, the depositions are confirmed to be PZT system oxide filmusing X-ray diffraction.

The deposition quantity of PZT system dielectric oxide on the platinumoxide substrate is compared with the deposition quantity of the presentinvention in the following TABLE 5 and TABLE 6.

For comparison, the same organic metal compound is dissolved in themethanol solution or acetone solution instead of the tetra-hydrofuran atthe same formation condition and using the same equipment. And the solidraw material organic metal compound without using organic solvent isused by CVD method.

As is apparent from TABLE 5, in case the raw material of the presentinvention is used, the deposition quantity of oxide film more than 10times is obtained in comparison with the conventional raw material,methanol solution or acetone solution for the first vaporizationexperiment. In case of the raw material of the present invention, quitestable deposition quantity is obtained for further continuousvaporization as same as the first embodiment. But, in case of other rawmaterials, the deposition quantity of the oxide film decreases forfurther number of continuous vaporization experiment. For more 15 timesof the vaporization experiment, the deposition quantity become zerobecause no further vaporization was occurred. As is apparent from TABLE6, in case the CVD raw material of the present invention is used, gooddeposition quantity of PZT system oxide film is obtained at anytemperature in comparison with the other three raw materials, becausethe present invention has good vaporization.

Embodiment 3

An experiment was carried out for evaluating characteristics of thecapacitors of the dielectric thin film comprising the strontium titanateoxide (SrTiO₃) formed on the magnesium-oxide substrate, the capacitor isused for the memory devices The experiment was carried out using the CVDequipment of the ordinary hot wall type having a three source system forheating the raw material. The raw material compound of the presentinvention is Sr acetyl-acetonate having 0.2 mol % concentration which isdissolved in the tetra-hydro-furan. Regarding Ti, conventionaliso-propoxide is used as the raw material compound. As film formationconditions, each raw material is bubbled by the argon gas as carrier gasand sent to the evaporator. The vapor temperature of the raw material isset to 195° C. for Sr and 190° C. for Ti. The reaction gas is set tooxygen, internal pressure of reactor (furnace) is set to 8 Torr,substrate temperature is set to 690° C. and reaction time is set to 10minutes.

After the reaction has finished, the substrate temperature is cooledspontaneously until the room temperature in the oxygen flow, then anoxide dielectric thin film having a thickness of approximately 50 nm isobtained. The crystallization is examined using X-ray diffraction, thenthe dielectric constant and the leak current density as capacitorproperties are measured by applying a DC voltage of 1.65 V to the film.

For comparison of the deposition quantity, Sr acetyl-acetonate and Tiiso-propoxide is used as a raw material organic metal compound, and sameformation condition and the same equipment is used for formingrespective oxide system dielectric films. But, since good vaporizationcan not be obtained for, especially, Sr, the vaporization temperature israised up to 280° C. in order to form the film. After the reaction isfinished, in the same way as carried out for the material of the presentinvention, the substrate temperature is cooled spontaneously until theroom temperature in the oxygen flow, then a film having a thickness ofapproximately 50 nm is obtained. The film characteristic and theperformance as capacitor are examined as well as the present invention.The result of the examination is shown in TABLE 7.

As is apparent from TABLE 7, according to the CVD raw material of thepresent embodiment, a dielectric thin film having good performance ascapacitor can be formed by CVD method at a lower heating temperaturethan the dielectric thin film formed of the conventional raw materialorganic metal compound. Comparing the film of the present embodimentwith the film manufactured by the conventional method, the leak currentbecomes less than one tenth for the same film thickness.

In the embodiment, the experiment is continuously repeated for 10 timesin order to examine the repeatability of the film in the same formationcondition described above. The result shows that there is littledeviation, such as less than ±5%, both for the dielectric constant andthe leak current density in the thin film manufactured from the CVD rawmaterial of the embodiment, and also it becomes clear that the method ofthe invention has good repeatability. On the contrary, the deviation ofboth dielectric constant and the leak current density for the capacitorfilm formed by the conventional method is very large, such as about±50%, against the value of TABLE 7.

Embodiment 4

Another experiment was carried out using the same CVD equipment of thefirst embodiment. In the second embodiment, the raw material compound isPb dipivaloyl-methanate, Zr dipivaloyl-methanate and Tidipivaloyl-methanate, which are dissolved in the tetra-hydrofuran toobtain material solutions of the present invention. The atom ratio ofthe respective metal atoms of the raw material compound is obtained by anext equation.

    Pb:Zr:Ti=2.2:1:1

The concentration is 0.55 mol % for the entire solution. The rawmaterial of the present embodiment is bubbled by the argon gas and sentto the evaporator and evaporated by heating at the temperature of 200°C. and then transported to the CVD reactor. The magnesium oxidesubstrate is used as a substrate, and substrate temperature is set to640° C. Under the above condition, PZT system oxide dielectric film isformed on the substrate. The thickness of the film was 89 nm.

For comparison, the conventional raw material organic metal compoundwhich is not dissolved in the tetra-hydrofuran is used for forming film.The respective temperatures are maintained at 250° C. for Pb, 230° C.for Zr and 210° C. for Ti, which are set at a higher temperature thanthat of the present invention. The thickness of the film was 150 nm. Theabove characteristics as capacitors for the two samples are shown inTABLE 8.

It is clearly understood from TABLE 8 as well as the embodiment 3 thatthe film of the present invention is thinner than that formed by theconventional material in spite of low temperature heating than that ofthe conventional method. And also a capacitor film formed by theoxide-system dielectric of the present invention has large dielectricconstant and small leak current density. For the present embodiment 3,the experiment is repeated for 10 times for examining the repeatabilityin the same condition described in the embodiment 3. The result showsthat the film formed from the material of the present embodiment 3 hasless deviation, such as less than ±5%, both for the dielectric constantand the leak current density in comparison with the thin film formedfrom the conventional material and also has good repeatability incomparison with the conventional deviation, such as about ±50%.

Embodiment 5

In the embodiment 5, the same CVD equipment as that of the embodiment 1is used and organic metal compound of Sr dipivaloyl-methanate, Badipivaloyl-methanate and Ti iso-propoxide are used as raw material forforming a barium-titanate-strontium-system-oxide-system dielectric thinfilm. All three kinds of the organic metal compounds are dissolved inthe tetra-hydrofuran so that the concentration of the total solutionbecomes 0.08 mol % (atom ratio of Sr, Ba, Ti=0.5, 0.5, 1.0). As aresult, one solution of the CVD raw material is obtained. The solutionis heated up to 210° C. and evaporated. Magnesium oxide is used as asubstrate. The temperature of the substrate is set to about 675° C. forobtaining an oxide dielectric film of Sr₀.5 Ba₀.5 TiO₃ having a filmthickness of 45 nm.

For comparison, the conventional raw material which is not dissolved inthe tetra-hydrofuran is used for forming film. In this case, the filmthickness is 70 nm. The respective temperatures are maintained at 285°C. for Sr, 280° C. for Ti, which are set at a higher temperature thanthat of the present invention from the same reason as explained in theembodiment 3. The above characteristics of the two samples as capacitorsare shown in TABLE 9.

It is clearly understood from TABLE 9 as well as the embodiment 3 and 4that the capacitor film is thinner than that formed by the conventionalraw material in spite of low temperature heating than that in theconventional raw material. And also an oxide-system dielectric thin filmof the present invention has large dielectric constant and small leakcurrent density. For the present embodiment 6, the experiment isrepeated for 10 times for examining the repeatability in the sameformation condition described in the embodiment 1. The result shows thatthe capacitor film formed by the material of the present embodiment 5has less deviation, such as less than ±5%, both for the dielectricconstant and the leak current density in comparison with the thin filmformed by the conventional material, and also has good repeatability incomparison with the film formed by the conventional method which is verylarge deviation such as about ±50%.

Two kinds of Sr dipivaloyl-methanate and Ti dipivaloyl-methanate in theabove three organic metal compounds are dissolved in thetetra-hydrofuran so that the concentration of the entire solute will be0.1 mol % (the atom ratio of Sr,Ti=1:1), and two kinds of Badipivaloyl-methanate and Ti dipivaloyl-methanate in the above threeorganic metal compounds are dissolved in the tetra-hydrofuran so thatthe concentration of the entire solute will be 0.2 mol % (the atom ratioof Ba,Ti=1:1), respectively, for obtaining two solutions of the presentinvention. Oxide dielectric films of SrTiO₃ and BrTiO₃ each having afilm thickness of 50 nm are obtained under the same condition for theabove-mentioned Sr₀.5 Ba₀.5 TiO₃.

For comparison, the conventional organic metal compound which is notdissolved in the tetra-hydrofuran is used for forming film. The filmsformed as capacitors by the above methods are shown in TABLE 10.

It is clearly understood from TABLE 10 as well as the embodiment 3 and 4that the capacitor film is thinner than that formed by the conventionalraw material in spite of low temperature heating than that in theconventional raw material. And also an oxide-system dielectric thin filmof the present invention has large dielectric constant and small leakcurrent density. For the present embodiment 6, the experiment isrepeated for 10 times for examining the repeatability in the sameformation condition described in the embodiment 1. The result shows thatthe capacitor film formed by the material of the present embodiment 5has less dispersion, such as less than ±5%, both for the dielectricconstant and the leak current density in comparison with the thin filmformed by the conventional material, and also has good repeatability incomparison with the film formed by the conventional method which is verylarge dispersion such as about ±50%.

Embodiment 6

In the embodiment 6, the same CVD equipment as that of the embodiment 1is used and organic metal compound of Sr dipivaloyl-methanate, Badipivaloyl-methanate and Ti iso-propoxide are used as raw material forforming a barium-titanate-strontium-system-oxide-system dielectric thinfilm. In case of the materials Sr and Ba, each dipivaloyl-methanatedielectric of Sr, Ba is dissolved in the tetra-hydrofuran by 0.35 mol %concentration to obtain two kinds of raw material. The raw material ofthe present embodiment is bubbled by the argon gas, which is carriergas, and sent to the evaporator and evaporated by heating at thetemperature of 210° C. and then transported to the reactor. Since Tiiso-propoxide is liquid raw material compound, it is heated up to 180°C. in order to vaporize. The magnesium-oxide is used as a substrate andthe substrate temperature is set to 655° C. and an oxide dielectric thinfilm having film thickness of 45 nm is obtained.

For comparison, the conventional raw material which is not dissolved inthe tetra-hydrofuran is used for forming film. In this case, the filmthickness is 125 nm. The respective temperatures are maintained at 235°C. for Sr, 255° C. for Ti, which are set at a higher temperature thanthat of the present invention. The above characteristics of the twosamples as capacitors are shown in TABLE 11.

It is clearly understood from TABLE 11 as well as the embodiment 3, 4and 5 that the capacitor film is thinner than that formed by theconventional raw material in spite of low temperature heating than thatin the conventional raw material. And also an oxide-system dielectricthin film of the present invention has large dielectric constant andsmall leak current density. For the present embodiment 6, the experimentis repeated for 10 times for examining the repeatability in the sameformation condition described in the embodiment 1. The result shows thatthe capacitor film formed by the material of the present embodiment 5has less deviation, such as less than ±5%, both for the dielectricconstant and the leak current density in comparison with the thin filmformed by the conventional material, and also has good repeatability incomparison with the film formed by the conventional method which is verylarge deviation such as about ±50%.

The above three organic metal compounds are all dissolved in thetetra-hydrofuran so that the concentration of the entire solute will be0.8 mol % (the atom ratio of Sr, Ba, Ti is 1:1:2) for obtaining CVD rawmaterial in one solution of the present invention. Using the abovesolution material, a barium-strontium titanate system dielectric thinfilm is formed in the same way as described above, and its performanceas a capacitor is examined. As a result, substantially the same and goodcharacteristic is obtained as well as TABLE 11.

In the above embodiments 3, 4 and 5, the largest reason of which theperformance of the capacitor using the oxide system dielectric filmformed from the conventional raw material organic metal compound is notgood, depends on the fact that the raw material compound is hard to bevaporized by heating and the raw material is dissolved by heating atrelatively high temperature, thereby the material compound is hard to betransported to the reactor. In other words, it is assumed that thelargest reason of which the performance of the oxide system dielectricfilm of the conventional raw material as a capacitor for memory devisesis not good, depends on ununiformity of formation of the formation filmcaused by unstable transportation for each raw material.

Using the raw material of the present invention, the thin film ofdielectric material such as PLZT, barium-titanate, tantalum-oxide,lead-titanate and bismuth-titanate is formed for several times using thesame raw material as well as the methods in the embodiments 1˜5. In anyoccasion, a dielectric thin film having a good performance as acapacitor is obtained with a good repeatability as well as the formerembodiments in comparison with the conventional method.

Many kinds of solvents are examined which dissolve the conventionalorganic metal raw material in the same methods of embodiments 1 and 2.The result shows that no improvement of vaporization, no stable effectof the material for multiple use and no stable vaporization effect isfound by heating at low temperature such as the tetra-hydrofuran used inthe present invention. Therefore, the tetra-hydrofuran have to be usedin the present invention for the organic solvent which dissolves theorganic metal compound. Organic solvent of the present invention may beany solvent which includes the tetra-hydrofiran more than 90 weight %,desirably any 5 solvent which includes the tetra-hydrofuran more than 95weight %, more desirably the solvent may include only tetra-hydrofuranWhen the tetra-hydrofuran becomes less than 90 weight %, it becomedifficult to obtain a desired heating vaporization characteristic and astability for a long period. The solvent may be any solvent whichdissolves well in the tetra-hydrofuran, for example, an alcohol groupsuch as methanol, ethanol, propanol, a ketone group such as acetonedimethyl-ketone, methyl-ethyl-ketone and benzene. The detailed effect ofthe tetra-hydrofuran is not clearly known, but it is assumed in view ofthe result of various examinations that the tetra-hydrofuran forms anycombination in addition to the organic metal compound, and the resultantproduct having good vaporization characteristic is formed.

Further in the present invention, the single organic metal compound maybe dissolved in the tertra-hydrofuran as shown in the embodiments 1, 2and 3 or many organic metal compound may be dissolved simultaneously toobtain one solution as shown in the embodiments 2 and 4. In thisoccasion, although the concentration of the organic metal compound inthe tetra-hydrofuran can not be defined uniformly since the solubilityis different for each material, it is able to select it in the range ofaround 0.001˜10 mol %. According to the above selection, an improvedeffect of the vaporization of the raw material is obtained as shown inany of above embodiments. The appropriate value of the concentration isabout 0.1˜1 mol % as indicated in the embodiment, but it is notrestricted within the above range.

It is confirmed that many kinds of raw material compounds used in thepresent invention can be used for a capacitor for memory devises whichis formed from the organic material compound of the dielectric oxide aswell as the former embodiments. It is also confirmed that, if a metalatom is a compound which is coupled together with an organic groupthrough oxygen atoms, a good effect can be attained for thetetra-hydrofuran as described above.

Therefore, in the present invention it is desirable to useacetyl-acetonate, dipivaloyl-methanate, alkoxide,hexafluoro-acetyl-acetonate, penta-fluoro-propanoil-pivaloyl-methanate,cyclopentadienyl and their derivatives. In the present invention,metoxide, etoxide, isopropoxide may be use as the alkoxide. In any abovecases, it is proved that above-mentioned good stability for a longperiod and improvement effect for vaporization are attained using thesolution in which they dissolve in the tetra-hydrofuran. Further, in theabove case, it is also proved that, if the metal atom is Pb, Ti, Zr oralkaline earth metal, more good performance as a capacitor can beobtained for the formed dielectric film. It is also proved that thesimilar performance is obtained in case of the metal atoms La, Ta or Bi.Sr, Ba may be used as the alkaline earth metal.

As shown in the embodiments 1˜5, it is proved that, if the metal atom ofthe organic metal raw material is at least one kind of selected metalsfrom Pb, Ti, Zr and alkaline earth metal, the effect of the presentinvention become better and better performance can be obtained for theformed dielectric capacitor film. Especially in case that the metal atomis Sr, Ba and Ti, and also in case that the metal atom is theirdipivaloyl-methanate system compound, dipivaloyl-methanate systemcompound of Sr and/or Ba and Ti iso-propoxide, it is proved that thestable effect for a long period and improved evaporation effect can beattained in the present invention.

                  TABLE 1                                                         ______________________________________                                        Deposition quantity (mg/cm.sup.2) of Sr oxide using organic Sr                  compound for a plurality of numbers of continuous vaporization                          first time                                                                             second time                                                                             fifth time                                                                           tenth time                              ______________________________________                                        solid raw material                                                                        0.11     0.08      0.05   0.01                                      (conventional method)                                                         methanol solution 0.12 0.09 0.04 0.03                                         acetone solution 0.12 0.10 0.06 0.01                                          THF solution 2.30 2.32 2.31 2.29                                              (present invention)                                                         ______________________________________                                    

                  TABLE 2                                                         ______________________________________                                        Deposition quantity (mg/cm.sup.2) of Sr oxide using organic Sr                  compound for a plurality of temperature of continuous vaporization                       180° C.                                                                         200° C.                                                                         220° C.                                                                       240° C.                          ______________________________________                                        solid raw material                                                                         0.02     0.05     0.11   0.24                                      (conventional method)                                                         methanol solution 0.01 0.06 0.12 0.23                                         acetone solution 0.02 0.05 0.12 0.21                                          THF solution 1.08 1.59 2.30 3.85                                              (present invention)                                                         ______________________________________                                    

                  TABLE 3                                                         ______________________________________                                        Deposition quantity (mg/cm.sup.2) of Ba oxide using organic Ba                  compound for a plurality of numbers of continuous vaporization                          first time                                                                             second time                                                                             fifth time                                                                           tenth time                              ______________________________________                                        solid raw material                                                                        0.10     0.08      0.03   0.01                                      (conventional method)                                                         methanol solution 0.11 0.09 0.03 0.02                                         acetone solution 0.09 0.10 0.06 0.01                                          THF solution 2.51 2.49 2.52 2.52                                              (present invention)                                                         ______________________________________                                    

                  TABLE 4                                                         ______________________________________                                        Deposition quantity (mg/cm.sup.2) of Ba oxide using organic Ba                  compound for a plurality of numbers of continuous vaporization                           180° C.                                                                         200° C.                                                                         220° C.                                                                       240° C.                          ______________________________________                                        solid raw material                                                                         0.02     0.05     0.10   0.19                                      (conventional method)                                                         methanol solution 0.01 0.06 0.11 0.22                                         acetone solution 0.02 0.05 0.09 0.19                                          THF solution 0.09 1.63 2.51 5.67                                              (present invention)                                                         ______________________________________                                    

                  TABLE 5                                                         ______________________________________                                        Deposition quantity (mg/cm.sup.2) of oxide using PZT raw material              for a plurality of numbers of continuous vaporization                                    first time                                                                             second time                                                                             fifth time                                                                           tenth time                              ______________________________________                                        solid raw material                                                                        0.31     0.29      0.24   0.21                                      (conventional method)                                                         methanol solution 0.32 0.30 0.23 0.20                                         acetone solution 0.33 0.29 0.24 0.21                                          THF solution 4.29 4.32 4.26 4.28                                              (present invention)                                                         ______________________________________                                    

                  TABLE 6                                                         ______________________________________                                        Deposition quantity (mg/cm.sup.2) of oxide using PZT raw material              for a plurality of temperature of continuous vaporization                                 180° C.                                                                         200° C.                                                                         220° C.                                                                       240° C.                          ______________________________________                                        solid raw material                                                                         0.22     0.31     0.46   0.66                                      (conventional method)                                                         methanol solution 0.22 0.32 0.49 0.63                                         acetone solution 0.24 0.33 0.48 0.67                                          THF solution 3.35 4.29 5.68 7.63                                              (present invention)                                                         ______________________________________                                    

                  TABLE 7                                                         ______________________________________                                                Equivalent           Leak current                                       film thickness Dielectric density                                             (nm) Constant (A/cm.sup.2)                                                  ______________________________________                                        Present Invention                                                                       0.83          230      1.2 × 10.sup.-8                          Conventional 0.91 210 8.0 × 10.sup.-7                                   Method                                                                      ______________________________________                                    

                  TABLE 8                                                         ______________________________________                                                Equivalent           Leak current                                       film thickness Dielectric density                                             (nm) Constant (A/cm.sup.2)                                                  ______________________________________                                        Present Invention                                                                       0.39          860      4.0 × 10.sup.-8                          Conventional 0.72 790 3.2 × 10.sup.-7                                   Method                                                                      ______________________________________                                    

                  TABLE 9                                                         ______________________________________                                                Equivalent           Leak current                                       film thickness Dielectric density                                             (nm) Constant (A/cm.sup.2)                                                  ______________________________________                                        Present Invention                                                                       0.65          410      1.0 × 10.sup.-8                          Conventional 0.83 320 6.0 × 10.sup.-7                                   Method                                                                      ______________________________________                                    

                  TABLE 10                                                        ______________________________________                                                Equivalent           Leak current                                       film thickness Dielectric density                                             (nm) Constant (A/cm.sup.2)                                                  ______________________________________                                        Present Invention                                                                       0.79          240      1.3 × 10.sup.-8                          (SrTiO.sub.3)                                                                 Conventional 0.95 200 9.0 × 10.sup.-7                                   Method (SrTiO.sub.3)                                                          Present Invention 0.97 195 2.2 × 10.sup.-8                              (BaTiO.sub.3)                                                                 Conventional 1.19 160 1.0 × 10.sup.-7                                   Method (BaTiO.sub.3)                                                        ______________________________________                                    

                  TABLE 11                                                        ______________________________________                                                Equivalent           Leak current                                       film thickness Dielectric density                                             (nm) Constant (A/cm.sup.2)                                                  ______________________________________                                        Present Invention                                                                       0.44          390      4.5 × 10.sup.-8                          Conventional 1.27 375 9.0 × 10.sup.-7                                   Method                                                                      ______________________________________                                    

What is claimed is:
 1. A method of forming a metal oxide dielectric thinfilm via chemical vapor deposition (CVD), comprising:dissolving at leastone organometallic CVD precursor compound in a solvent system includingtetrahydrofuran to form a liquid solution; vaporizing the liquidsolution including the at least one organometallic compound; and formingthe metal oxide dielectric thin film by depositing at least a portion ofthe at least one organometallic compound from the vaporized solution ona substrate.
 2. The method as recited in claim 1, wherein the at leastone organometallic compound includes a species selected from the groupconsisting of Pb, Ti, Zr and alkaline earth metals.
 3. The method asrecited in claim 2, wherein the at least one organometallic compoundincludes an organic group coupled to a metal atom through an oxygenatom.
 4. The method as recited in claim 1, wherein the at least oneorganometallic compound includes an organic group coupled to a metalatom through an oxygen atom.
 5. The method as recited in claim 4,wherein the at least one organometallic compound comprises a firstorganometallic compound having a metal atom selected from the groupconsisting Sr and Ba, and a second organometallic compound including Ti.6. The method as recited in claim 4, wherein the at least oneorganometallic compound includes a metal selected from the groupconsisting of Pb, Ti, Zr and alkaline earth metals, and includes atleast one ligand selected from the group consisting of acetyl-acetonate,dipivaloyl-methanate, alkoxides, hexafluoro-acetyl-acetonates,pentafluoro-propanoil-pivaloyl-methanates, and cyclopentadienyl.
 7. Themethod as recited in claim 5, wherein the first organometallic compoundcomprises an organometallic compound including a metal selected from thegroup consisting Sr and Ba, and the second organometallic compoundcomprises a Ti dipivaloyl-methanate system compound.
 8. The method asrecited in claim 5, wherein the first organometallic compound comprisesa dipivaloyl-methanate system having a metal selected from the groupconsisting Sr and Ba, and the second organometallic compound comprisesTi alkoxide.
 9. The method as recited in claim 5, wherein the firstorganometallic compound comprises a dipivaloyl-methanate system having ametal selected from the group consisting Sr and Ba, and the secondorganometallic compound comprises Ti iso-propoxide.
 10. The method asrecited in claim 4, wherein the at least one organometallic compound isselected from the group consisting of acetyl-acetonates of metalsselected from the group consisting of Pb, Ti, Zr and alkaline earthmetals, dipivaloyl methanates of metals selected from the groupconsisting of Pb, Ti, Zr and alkaline earth metals, alkoxides of metalsselected from the group consisting of Pb, Ti, Zr and alkaline earthmetals, hexafluoro-acetyl-acetonates of metals selected from groupconsisting of Pb, Ti, Zr and alkaline earth metals,pentafluoro-propanoil-pivaloyl-methanates of metals selected from thegroup consisting of Pb, Ti, Zr and alkaline earth metals,cyclopentadienyl of metals selected from the group consisting of Pb, Ti,Zr and alkaline earth metals, and one or more derivatives of theseorganometallic compounds.
 11. The method as recited in claim 1, whereinthe solvent system includes at least 90 weight % tetrahydrofuran. 12.The method as recited in claim 11, wherein the solvent system includesat least 95 weight % tetrahydrofuran.
 13. The method as recited in claim12, wherein the solvent system includes substantially puretetrahydrofuran.
 14. The method as recited in claim 1, wherein thevaporizing step comprises heating the solvent system at a temperatureless than a decomposition temperature of the at least one organometalliccompound in the presence of a carrier gas.
 15. The method as recited inclaim 14, wherein the depositing step comprises contacting the vaporizedorganometallic compound with a substrate heated to a predeterminedtemperature.
 16. The method as recited in claim 15, wherein thesubstrate comprises magnesium oxide.
 17. The method as recited in claim15, wherein the depositing step comprises contacting the vaporizedorganometallic compound with the substrate in the presence of oxygen.18. The method as recited in claim 1, wherein the vaporizing stepcomprises heating the solvent system in which is dissolved the at leastone organometallic CVD precursor to a temperature of from about 180° C.to about 240° C. in hot wall CVD apparatus.
 19. The method as recited inclaim 1, including vaporizing the liquid solution by bubbling a carriergas through the liquid solution.